1. Technical Field
This invention relates to the field of microwave filters and resonators.
2. Description of the Related Art
A microwave filter is an electromagnetic circuit that can be tuned to pass energy at a specified resonant frequency. The filter is used in communications applications to filter a signal by removing frequencies that are outside a bandpass frequency range. This type of filter typically includes an input port an output port, and a filter cavity. The bandpass filtering properties of the filter are determined by the size and shape of the filter cavity and by the coupling effects of the filter to the electromagnetic signal.
In many filter applications, it is desirable to filter the signal by passing it through multiple cavities in series. In such an application, it is necessary to form an iris between adjacent cavities to pass the energy from the first cavity to the second cavity. The iris is typically formed on a common wall of both cavities.
A microwave filter is provided that includes a first filter cavity with a wall centered on a first axis and a second filter cavity with a wall centered on a second axis. The first and second axes are parallel to each other. A central iris is configured and oriented along the wall of the first cavity and extends through the wall of the second cavity. A pair of peripheral irises are equidistantly spaced circumferentially from the central iris. The peripheral irises extend from the wall of the first cavity to the wall of the second cavity. The peripheral irises couple a primary mode of an input electromagnetic signal from the first cavity to the second cavity and the central iris couples a secondary mode of the same input electromagnetic signal from the first cavity to the second cavity.